Photographic enlargers include a light source which emits light beams for illuminating a film negative for an enlarger lens which will reproduce the image on the film negative on selected printing paper. Light beams from the light source may not be uniformly distributed. In the case of photographic enlargement with color, color compensating filters such as plastic, geltin, or dichroic filters, are employed to color correct the light to provide a desired color photograph. Light mixing means and/or light diffusing means are employed to provide more uniform illumination of a film negative. After mixing, light beams traveling along the axis of the light path generally provided greater light intensity at the central portion of the film negative than at peripheral margins thereof.
Prior proposed light mixing and diffusing means have included the use of a flat disk in the central portion of the light path to prevent direct light from the light source from impinging upon the film negative plane. Intensity of light at the peripheral margins was not changed and was of insufficient intensity to compensate for the cosine 4 fall off of the enlarger lens. The image on the film negative transmitted by the enlarger lens under such circumstances was not seen by the enlarger lens under conditions of uniform light intensity over the film negative plane. As a result, a photographic print made under such conditions was nonuniformly exposed.
Another proposed construction of a light diffusing means included use of a rectangular cylinder light diffusing chamber having parallel walls with a conical or semi-spherical outwardly directed reflecting surface provided on an element within the chamber to redistribute light admitted into the chamber to improve the intensity of light in the peripheral areas of the film negative. Different light reflecting surfaces were provided on the chamber walls to cooperate with the conical light reflecting surface to provide such improved light intensity distribution. See U.S. Pat. No. 3,927,941.